An object recognition requires to extract a particular mask area within a subject image in order to validate the mask area by comparison with an object image template. There have been proposed a scheme for extraction of the mask area, for example, as disclosed in US2001-002932 and JP09-73544.
US2001-002932 discloses a human face image extraction system which selects a suitable template in order to extract the mask area from within the subject image that matches with the template. The template is selected to include a circular, ellipse, or polygon in anticipation of that the human face has a contour analogous with such simple shape. However, with the use of such simple shape as the template, it is likely to miss the mask area and is therefore not reliable for extracting the true mask area to be validated.
JP09-73544 discloses a like system which utilizes a template of ellipse and varies parameters of the ellipse to get an optimum ellipse in best match with the mask area to be validated. This scheme necessitates selecting a temporary mask area each time the parameters are varied to give an instant ellipse, and analyzing a correlation between the temporary mask area and instant ellipse until the correlation satisfies a predetermined criterion. Therefore, the scheme requires a large number of arithmetic operations in order to obtain the optimum parameters, i.e., the optimum ellipse in best match with the mask area to be validated, and is not suitable for rapid human face recognition.